The present invention relates to the field of an apparatus for minimizing or eliminating by-product accumulation in the exhaust lines of reactors used for electronic device fabrication.
Many of the films used in electronic device fabrication today are formed in deposition reactors similar to reactor 100 shown in FIG. 1. In deposition reactor 100, lamps 105 provide radiant heat to wafer 110 which is supported within reactor 100 by rotating susceptor 115. Process and cleaning gases are provided via gas inlet conduit 120 and inlet manifold 125. Gases are exhausted via exhaust manifold 130 and exhaust conduit 135. Exhaust conduit 135 is in communication with reactor 100 and the remaining exhaust systems 140 located within the wafer fabrication facility. Exhaust systems 140 may contain scrubbers, filtration units as well as other exhaust treatment systems.
During deposition and cleaning processes conducted with reactor 100, lamps 105, or alternative heat sources utilized by other types of semiconductor processing reactors, heat not only rotating susceptor 115 and wafer 110 but also gas inlet 125 and exhaust manifold 130. As a result, lamps 105 or other chamber heat sources also heat approximately 2-3 cm of exhaust conduit 135 located directly adjacent to exhaust manifold 130.
Additionally, hot gases exhausted by reactor 100 also heat conduit 135. Generally, as the processing temperature within reactor 100 increases the length of conduit 135 heated by hot exhaust gases increases. For example, in a deposition reactor 100 depositing silicon film by thermal CVD at, for example, 600 C., as much as about 2 to 3 feet of conduit 135 could be heated above room temperature or about 70 F. by exhausting deposition gases. Additionally, conduit 135 could be heated because of the cleaning processes used to clean reactor 100 after deposition. One representative cleaning process for the silicon deposition process described above is to raise reactor 100 above about 900 C. and inject HCl into reactor 100. The exhaust from such a high temperature cleaning process could be expected to raise the temperature of about 3-6 feet of conduit 135.
Referring to FIG. 1, that portion of exhaust conduit 135 heated by a combination of reactor heat sources, such as lamps 105, and heated reactor exhaust is labeled Zone A. Zone A is that portion of exhaust conduit 135 between exhaust manifold 130 and the dashed line, representing 2-3 cm beyond exhaust manifold 130, where hot exhaust gases as well as chamber heating sources, such as lamps 105, contribute to the heating of conduit 135.
Zone B of FIG. 1, shown between the dashed lines, represents that portion of conduit 135 heated by the hot exhaust gases of reactor 100. The temperature of conduit 135 within Zone B remains above the ambient temperature surrounding conduit 135. Zone B could include several feet of conduit 135 depending upon the temperature and flow rate of the exhausting gases. Zone C represents that portion of conduit 135 where the temperature is essentially the same as the surrounding ambient conditions.
Although conduit 135 within Zone B remains above the surrounding ambient temperature, at some point the temperature within conduit 135 decreases below the condensation points of the vapors contained in the exhaust of reactor 100. This condensation region, labeled CR on FIG. 1, delineates where gaseous by-products may condense to form deposits along the internal walls of conduit 135. Upstream of CR towards reactor 100, conduit 135 contains mostly vapor while downstream of CR conduit 135 contains a mixture of vapor and condensing by-products 145. Condensation continues within conduit 135 beyond condensation region CR so long as the temperature within conduit 135 remains below the condensation temperature of by-products 145. After condensation, many by-products will further polymerize along the interior walls of conduit 135. Reference number 145 indicates condensed, polymerized by-products formed along the interior walls of conduit 135.
Deposition processes conducted within reactor 100 result in desired deposits on substrate 110 as well as undesired film formation on internal surfaces and components of reactor 100. Additionally, some source gases, such as SiH4 or chlorinated silanes from the previous example, exhaust unreacted from deposition reactor 100. As unreacted source gases exit reactor 100, temperatures within exhaust manifold 130 and exhaust conduit 135 within Zone A are typically high enough such that the unreacted gases can remain in the vapor phase. However, beyond the condensation region CR, unreacted source gases can also condense, polymerize and contribute to the accumulation of by-products 145 along the interior walls of conduit 135.
During the cleaning process, cleaning gases are introduced into reactor 100 to remove unwanted deposits from internal reactor components. As these deposits are removed from reactor 100 and are exhausted via exhaust manifold 130 into exhaust conduit 135, the unwanted deposit/cleaning gas mixture can behave similarly to the unreacted source gas. Within Zone A, a portion of the unwanted deposit/cleaning gas mixture remains gaseous, does not form deposits, condense or polymerize on the interior walls of exhaust conduit 135. As a result of the higher temperatures used during cleans, temperatures within Zone A and some of Zone B will be high enough such that a portion of the unreacted cleaning gas exhausting from reactor 100 will remain active. Thus, within that region where the unreacted cleaning gas remains active, the unreacted cleaning gas will be able to react with and remove by-products 145 deposited within that active cleaning gas area of conduit 135.
However, like the exhaust from the deposition process, the exhaust from the cleaning process will eventually cool within the condensation region CR, to a temperature where it is likely that most of the cleaning gas or gases will be inactive. Beyond CR, exhaust from the cleaning process will also contribute to the accumulation and further polymerization of by-products 145. Thus, within Zone A, reactor heating sources and high exhaust gas temperatures can result in sufficient temperatures within conduit 135 where most deposits formed will likely be removed by unreacted but still active cleaning gases. Within Zone B however, temperatures will likely not be high enough for any remaining unreacted cleaning gas to remain active. As described above, downstream of the condensation region, conditions within conduit 135 are such that the mixture of cleaning gas/by-product removed from Zone A, and the mixture of cleaning gas/deposits removed from reactor 100 can condense, polymerize and contribute to the accumulation of by-products 145 within conduit 135.
The problem currently faced by many types of reactors is the condensation and polymerization of unreacted source gas, cleaning gas/by-product mixture and cleaning gas/unwanted deposition mixture which result in the constant, gradual formation of highly viscous liquid or solid by-product 145 along the interior walls of exhaust conduit 135. As a result of this by product build up, exhaust conduit 135 becomes partially blocked thereby reducing reactor exhaust flow efficiencies and, in the case of reduced pressure systems, reducing vacuum pump performance. On a regularly occurring basis, by-product accumulation within conduit 135 becomes so substantial that the reactor 100 must stop production, exhaust conduit 135, or the blocked portion therein, must be disconnected from reactor 100 and the accumulated by-product removed.
These and other disadvantages of the prior art are overcome by the present invention directed to a method and an apparatus which can inhibit or eliminate by-product condensation and polymeric formation within exhaust lines. Such an apparatus minimizes exhaust line blockages, maximize reactor up-time, and enables longer time between service for reactor exhaust systems.
In accordance with the present invention, there is disclosed a method and apparatus for removing wafer processing by-products from a fluid conduit or exhaust channel which is attached to a substrate processing area by placing an energy source, such as heaters or UV lamps, within the exhaust channel. The placement of this energy source provides energy internal to an exhaust conduit such that the viscosity of polymeric by-products would be reduced whereby the by-product material can flow, or partially or fully vaporize, or recombine or react in the presence of a cleaning gas to form gaseous by-products. The resulting gaseous by-products can therefore be more expeditiously and completely removed by gaseous fluid exhaust systems. More precisely, the present invention is directed to an improved method and apparatus for adding energy internal to the exhaust conduit of a wafer processing reactor in order to minimize condensation and polymerization of deposition and cleaning by-products as well as promote more thorough removal of deposition and cleaning by-products from the reactor""s exhaust system.
In an alternative embodiment of the present invention, a gas supply feature is provided to a fluid conduit exhaust channel in proximity to the energy source within the exhaust channel whereby a cleaning gas or combination of gases such as Cl2, HCl, ClF3, F2, NF3 or O3, can be introduced into the exhaust channel. In this way, the cleaning gas or mixtures thereof can react or recombine with or otherwise break down by-products present within the conduit to form gaseous by-products which are more easily removed by exhaust treatment systems. With the addition of the gas supply feature, the cleaning gas or combinations of cleaning gases utilized in conjunction with the energy provided by the internal energy source provide an additional process which can be used to react, recombine, or otherwise break down by-products present within the exhaust conduit to form gaseous by-products.
A major objective of the present invention is that the energy and cleaning gas in the exhaust conduits of the present invention provide an opportunity to reduce the formation of solid or highly viscous by-products and convert by-products into less viscous or gaseous by-products within the gas fluid exhaust conduits of wafer processing systems. Minimizing by-product formation and accumulation within chamber exhaust systems leads to enhanced wafer throughput by reducing or eliminating the necessity of ceasing chamber operations to dissemble, remove by-product accumulations and re-install chamber exhaust lines. Wafer fabrication exhaust treatment system efficiency and ability to remove and properly dispose of chamber exhaust by-products are increased by providing methods and apparatuses which result in gaseous chamber by-product formation.